1. Field of the Invention
The present invention relates to a socket configured to electrically connect a connecting item, such as a semiconductor package, to a substrate, such as a circuit board, and to a method of fabricating such a socket.
2. Description of the Related Art
Conventionally, there is a socket configured to electrically connect a connecting item to a circuit board or the like. FIG. 1 is a cross sectional view illustrating a first example of a conventional socket. As illustrated in FIG. 1, a conventional socket 100 includes a support member 101, and conductive connecting terminals 102 and 103 that are flexible and have a spring property. A plurality of through holes 101x are arranged at a predetermined pitch in the support member 101. A wiring 104 is formed on one surface 101a of the support member 101, and the wiring 104 extends from the one surface 101a to another surface 101b of the support member 101 via the through hole 101x. 
One end of the connecting terminal 102 is fixed to the wiring 104 formed on the one surface 101a of the support member 101. The other end of the connecting terminal 102 may contact a pad 401 of a connecting item 400. For example, the connecting item 400 may be a wiring board, a semiconductor package, and the like. One end of the connecting terminal 103 is fixed to the wiring formed on the other surface 101b of the support member 101. The other end of the connecting terminal 103 is electrically connected to a circuit board 500, such as a mother board. The connecting terminals 102 and 103 may be formed by identical parts.
When the connecting item 400 is pushed towards the socket 100 with the pad 401 facing the socket 100, the other end of the connecting terminal 102 makes contact with the pad 401 to electrically connect the socket 100 and the connecting item 400. In other words, the connecting item 400 is electrically connected to the circuit board 500 via the socket 100, as proposed in a U.S. Pat. No. 7,371,073, for example.
FIG. 2 is a cross sectional view illustrating a second example of the conventional socket. In FIG. 2, those parts that are the same as those corresponding parts in FIG. 1 are designated by the same reference numerals. As illustrated in FIG. 2, a conventional socket 200 includes conductive connecting terminals 202 in place of the connecting terminals 102 of the socket 100 illustrated in FIG. 1. The connecting terminals 202 are flexible and have a spring property. One end of the connecting terminal 202 is fixed to the wiring 104 formed on one surface 101a of the support member 101. The other end of the connecting terminal 202 may connect to the pad 401 of the connecting item 400. Unlike the socket 100 illustrated in FIG. 1, the socket 200 includes bumps 203 in place of the connecting terminals 103. The wiring 104 formed on the other surface 101b of the support member 101 is electrically connected to the circuit board 500 via the bump 203.
When the connecting item 400 is pushed towards the socket 200 with the pad 401 facing the socket 200, the other end of the connecting terminal 202 makes contact with the pad 401 to electrically connect the socket 200 and the connecting item 400. In other words, the connecting item 400 is electrically connected to the circuit board 500 via the socket 200, as proposed in a Japanese Patent No. 3157134, for example.
FIG. 3 is a cross sectional view illustrating a third example of the conventional socket. In FIG. 3, those parts that are the same as those corresponding parts in FIG. 1 are designated by the same reference numerals. As illustrated in FIG. 3, a conventional socket 300 includes a housing 301 made of a resin, and conductive connecting terminals 302 that have a spring property.
A plurality of penetrating holes 301x are arranged at a predetermined pitch in the housing 301. The connecting terminal 302 includes connecting parts 315 and 316 and a spring part 317 that are integrally formed, and is fixed or fit within the penetrating hole 301x in the housing 301. The connecting part 315 projects from one surface 301a of the housing 301, and the connecting part 316 is exposed from the other surface 301b of the housing 301.
The connecting part 316 is electrically connected to the circuit board 500 via a bump 303. When the connecting item 400 is pushed towards the socket 300 with the pad 401 facing the socket 300, the connecting part 315 makes contact with the pad 401 to electrically connect the socket 300 and the connecting item 400. In other words, the connecting item 400 is electrically connected to the circuit board 500 via the socket 300, as proposed in a U.S. Pat. No. 7,264,486, for example.
In the socket 100 illustrated in FIG. 1, the connecting terminals 102 and 103 are respectively formed on the two surfaces 101a and 101b of the support member 101. In addition, the connecting terminal 102, the wiring 104 including the wiring formed within the through hole 101x, and the connecting terminal 103 form a signal transmission path between the connecting item 400 and the circuit board 500. For this reason, as the height of the socket 100 becomes higher, the connecting distance, that is, the length of the signal transmission path, between the connecting item 400 and the circuit board 500 becomes longer. According to the socket 100 having the structure described above, it may be difficult to reduce the height of the socket 100 which in turn may interfere with high-speed signal propagation.
On the other hand, in the socket 200 illustrated in FIG. 2, the connecting terminal 202 is formed on one surface 101a of the support member 101. In addition, the connecting terminal 202, the wiring 104 including the wiring formed within the through hole 101x, and the bump 203 form a signal transmission path between the connecting item 400 and the circuit board 500. The height of the socket 200 may be lower than that of the socket 100 by an amount corresponding to the replacement of the connecting terminal 103 by the bump 203. Moreover, the connecting distance, that is, the length of the signal transmission path, between the connecting item 400 and the circuit board 500, may be reduced when compared to the socket 100. However, the height of the socket 200 may not be reduced considerably due to the provision of the connecting terminal 202 and the support member 101. Further, a signal from the connecting item 400 to the circuit board 500 propagates through the wiring 104 formed within the through hole 101x of the support member 101, and thus, the connecting distance, that is, the length of the signal transmission path, between the connecting item 400 and the circuit board 500, may not be reduced considerably.
In the socket 300 illustrated in FIG. 3, no wiring is formed within the penetrating hole 301 of the housing 300, and only the bump 303 and a part of the connecting terminal 302 fixed within the penetrating hole 301x make contact with the circuit board 500 and the connecting item 400. It may appear as if the height of the socket 300 may be reduced sufficiently, and that the connecting distance, that is, the length of the signal transmission path, between the connecting item 400 and the circuit board 500, may be reduced sufficiently.
However, the part of the connecting terminal 302, that is fixed or fit within the penetrating hole 301x, does not function as a spring. Only the part of the connecting terminal 302 projecting from the one surface 301a of the housing 301 may primarily function as a spring. Consequently, in order for the connecting terminal 302 to sufficiently function as a spring, the part of the connecting terminal 302, projecting from the one surface 301a, must have a sufficiently long length. In addition, in order to fix or fit the part of the connecting terminal 302 within the penetrating hole 301a, the housing 301 must be thick to a certain extent. As a result, the height of the socket 300 may not be sufficiently reduced, and the connecting distance, that is, the length of the signal transmission path, between the connecting item 400 and the circuit board 500, may not be reduced considerably.